This invention is for an improved mine roof support and is particularly although not exclusively applicable to a mine roof support having hydraulically extensible prop or jack means for applying a roof-engaging member or canopy to and holding it against the roof to be supported. Such a support is frequently made self-advancing in which case it may also incorporate pressure-fluid ram means connected between the support and a mineral face conveyor. After having advanced the conveyor, towards the mineral face being worked, the ram means is operated, using the conveyor as an anchorage, to advance the roof support, the prop means having temporarily been released from between floor and roof. Alternatively the ram means may be connected between two similar roof supporting units of the support, each unit serving in turn as an abutment or anchorage for the advance of other when the latter has been temporarily released from between floor and roof.